In radio communication systems such as WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution), and LTE-A (LTE-Advanced) by 3GPP (Third Generation Partnership Project), and Wireless LAN, and WiMAX (Worldwide Interoperability for Microwave Access) by IEEE (The Institute of Electrical and Electronics engineers), each of the base stations (cell, transmitting station, transmitter apparatus, eNodeB) and the terminals (mobile terminal, receiving station, mobile station, receiver apparatus, UE (User Equipment)) comprises a plurality of transmit and receive antennas and spatial-multiplexes data signals, and performs high-speed data communication using MIMO (Multi Input and Multi Output) technique.
In order to perform data communications between a base station and a terminal in a radio communication system, the base station needs to perform a variety of control processes for the terminal. To this end, the base station performs data communications with the terminal in a downlink and an uplink by notifying the terminal of control information using a predetermined resource. For example, the base station performs data communications by notifying the terminal of resource allocation information, modulation and encoding information of a data signal, spatial multiplexing count information of the data signal, transmission power control information, and the like. The method described in Non-Patent Literature may be used to notify the control information.
A variety of methods may be used as a communication method based on the MIMO technique in the downlink. For example, the communication methods that may be used comprise the multi-user MIMO scheme that allocates the same resource to different terminals, and the CoMP (Cooperative Multipoint or Coordinated Multipoint) scheme that performs data communications with a plurality of base stations in cooperation with each other.
FIG. 34 illustrates an example of the multi-user MIMO scheme. As illustrated in FIG. 34, a base station 3401 performs data communications with a terminal 3402 in a downlink 3404, and performs data communications with a terminal 3403 in a downlink 3405. The terminal 3402 and the terminal 3403 perform data communications using the multi-user MIMO. The same resource is used in the downlink 3404 and the downlink 3405. The resource comprises a resource in the frequency domain and the time domain. By using the precoding technique and the like, the base station 3401 controls a beam forming toward each of the downlink 3404 and the downlink 3405, thereby maintaining mutual orthogonality or reducing the interference between the same type of channels. In this way, the base station 3401 performs data communications with the terminal 3402 and the terminal 3403 using the same resource.
FIG. 35 illustrates an example of the downlink CoMP scheme. As illustrated in FIG. 35, a radio communication system is constructed using a heterogeneous network comprising a macro base station 3501 having a wide coverage area, and an RRH (Remote Radio Head) 3502 having a coverage area narrower than the coverage area of the macro base station 3501. The following discussion is based on the assumption that the coverage area of the macro base station 3501 comprises whole or part of the coverage area of the RRH 3502. In the example of FIG. 35, the macro base station 3501 and the RRH 3502 form a heterogeneous network, and coordinate with each other, thereby performing data communications with a terminal 3504 in a downlink 3505 and a downlink 3506. The macro base station 3501 is connected with the RRH 3502 via a communication line 3503 and exchanges the control signal and the data signal with the RRH 3502. A wired line, such as an optical fiber, or a wireless line based on relay technique may be used for the communication line 3503. Whole or part of each of the macro base station 3501 and the RRH 3502 may use the same frequency (resource), and overall frequency usage efficiency (transmission capacity) in the coverage area of the macro base station 3501 may increase.
The terminal 3504, if located closer to the macro base station 3501 or the RRH 3502, may communicate with the macro base station 3501 or the RRH 3502 in single cell communication. If the terminal 3504 is located in the vicinity of the edge of the coverage area (cell edge) of the RRH 3502, a corrective step to the same channel interference from the macro base station 3501 becomes necessary. Currently under study is a method of reducing or suppressing interference to the terminal 3504 at the cell edge by using the CoMP scheme. In the CoMP scheme, the macro base station 3501 and the RRH 3502 cooperate with each other in multi-cell communication (coordinated communication) between the macro base station 3501 and the RRH 3502. The method described in Non-Patent Literature 2 is currently under study as the CoMP scheme.
FIG. 36 is an example of the uplink CoMP scheme. As illustrated in FIG. 36, a radio communication system is constructed using a heterogeneous network comprising a macro base station 3601 having a wide coverage area, and an RRH (Remote Radio Head) 3602 having a coverage area narrower than the coverage area of the macro base station 3601. The following discussion is based on the assumption that the coverage area of the macro base station 3601 comprises whole or part of the coverage area of the RRH 3602. In the example of FIG. 36, the macro base station 3601 and the RRH 3602 form a heterogeneous network, and coordinate with each other, thereby performing data communications with a terminal 3604 in an uplink 3605 and an uplink 3606. The macro base station 3601 is connected with the RRH 3602 in a communication line 3603 and exchanges the control signal and the data signal with the RRH 3602. A wired line, such as an optical fiber, or a wireless line based on relay technique may be used for the communication line 3603. Whole or part of each of the macro base station 3601 and the RRH 3602 may use the same frequency (resource), and overall frequency usage efficiency (transmission capacity) in the coverage area of the macro base station 3601 may increase.
The terminal 3604, if located closer to the macro base station 3601 or the RRH 3602, may communicate with the macro base station 3601 or the RRH 3602 in single cell communication. In this case, with the terminal 3604 located closer to the macro base station 3601, the macro base station 3601 receives and demodulates a signal received in the uplink 3605. With the terminal 3604 located closer to the RRH 3602, the RRH 3602 receives and demodulates a signal received in the uplink 3606. With the terminal 3604 located at the edge (cell edge) of the coverage area of the RRH 3602 or located at the midpoint between the macro base station 3601 and the uplink 3605, the macro base station 3601 receives a signal passing through the uplink 3605 and the RRH 3602 receives a signal passing through the uplink 3606. Using the communication line 3603, the macro base station 3601 and the RRH 3602 then transmit and receive the signals received from the terminal 3604, and combine the signals received from the terminal 3604, and demodulate a combined signal. Through these operations, performance improvements are expected. This method is referred to as Joint Reception. The CoMP scheme with the macro base station 3601 and the RRH 3602 in cooperation is used as an uplink multi-cell (multipoint) communication (also referred to as coordinated communication). As a result, performance improvements are possible in data communications in the cell edge area, or at the midpoint area between the macro base station 3601 and the RRH 3602.